The crudest form of a prosthesis is a hard, stump-receiving socket. If a socket is for receiving the stump of a below-the-knee amputee, it will be attached by suitable means to a prosthetic foot; if it is for an above-the-knee amputee, it will be attached to a prosthetic knee as well. In either application, the amputee will experience discomfort arising from contact between the stump and the hard interior of the stump,receiving socket unless an adequate cushioning means is provided.
Some prosthetic devices are held onto the residual limb (amputation stump) by suction. A one way valve releases air from the socket as the residual limb is inserted thereinto. When the residual limb is fully inserted, the tissue is pulled slightly downwardly and this creates a suction within the socket that holds it on. Obviously, this suction must be maintained if the socket is to remain in place.
Some individuals fit socks over their residual limb in an attempt to make the prosthesis more comfortable. Several layers of socks will form a reasonably soft cushion, but there are a number of drawbacks to the use of socks as socket liners. Perhaps the most obvious limitation is the inability of socks to protect a particular point or area where extra cushioning is needed, i.e., socks provide the same amount of cushioning everywhere. Moreover, the diameter of a stump will vary during the day, especially where the amputee is active. Specifically, most stumps shrink in size as the day progresses because walking and other activities literally drives blood and other fluids out of the stump; this results in the need for more layers of socks and that need requires the amputee to travel throughout the day with a supply of extra socks on hand. It is also troublesome and time-consuming to remove the socket, add a layer or two of socks, and to reattach the socket several times per day. Amputees who use socks as cushioning means are of course familiar with other drawbacks not mentioned herein.
Perhaps even more problematic than daily stump volume variations are the long term variations brought about by long term weight loss or weight gain.
In response to the limitations of socks as a means for cushioning, inventors have developed a number of alternatives thereto. Perhaps the simplest, most obvious alternative is to line the socket with a cushioning means. The problem with cushioned stump-receiving sockets is equally obvious, i.e., the fit between the socket and the stump becomes loose as the day progresses, and the amputee must again resort to the expedient of employing multiple layers of socks to maintain a reasonably tight fit as required.
Cushioned sockets, like socks, also fail to provide extra cushioning to particular points or areas.
Accordingly, customized cushioning means have been developed so that each individual amputee may have a cushioning means that matches the contour of his or her residual limb. A cast is made of the stump by wrapping plaster bandages around it, or by simply inserting the stump into a vat of impressionable material. The negative of the stump thereby created is then filled with plaster or other suitable material; this produces a replica of the residual limb. A liner is then fabricated that provides the proper amount of cushioning at the places where extra cushioning is needed.
Although liners so fabricated are superior in performance to socks and non-customized liners, they do not compensate for the changes in size of the stump during a day or from day to day. Moreover, such liners are expensive because they must be made for one patient at a time.
In an attempt to provide customized liners that compensate for changes in stump size, inventors have developed liners that include inflatable bladders. Thus, as the day progresses, more air is introduced into preselected bladders to maintain the tight fit between the socket and stump and to maintain the amputee's comfort level.
Even these advanced liners have shortcomings. Their primary drawback is that they must be customized with a high degree of precision for each patient. Thus, they cannot be mass produced and their unit cost is therefore quite high. In U.S. Pat. No. 4,923,475 to Gosthnian et. al., the stump-engaging surface of each bladder is molded to have a shape conforming to the outer surface of the amputee's stump when the stump is under static pressure, i.e., the patient stands to place static pressure on the stump, and the bladders are made so that they conform, when inflated, to the particular contour of the stump thereby produced. This highly exacting procedure does not lend itself to mass production.
U.S. Pat. No. 4,923,474 to Klasson et. al. discloses a liner that has a distal end that is highly elastic in a radial direction so that it tightly and snugly engages the stump as the stump changes size, yet which is substantially inelastic axially so that it is easy to position. No bladders are provided,
Thus, to those of ordinary skill in this art, it would appear that liners employing bladders and bladder-free liners have reached a state of such advanced development that the only advances that will be made in the future will relate to better materials, better production techniques, and the like. Nothing whatsoever in the art suggests that liners having inflatable bladders could be mass produced yet precisely fit to individual patients.